This application claims benefit of priority under 35 U.S.C. xc2xa7119 to Japanese Patent Application No. 11-202818, filed on Jul. 16, 1999, the entire contents of which are incorporated by reference herein.
1. Field of the Invention
The present invention relates to an antenna assembly comprising a hexahedron of a dielectric material on the surface of which a patterned conductive film is formed.
2. Description of the Related Art
While small size mobile communication sets such as a cordless telephone have been frequently used in recent years, antennas to be used in these communication sets are required to be compact, highly precise and cheap as other electronic components are.
The main body of this antenna is assembled so that a desired pattern of a conductive film is formed on each surface of a hexahedron of a dielectric material. The conductive film has been formed either by printing, plating, vapor deposition or sputtering.
In the printing method, however, a complicated and inefficient procedure was required since the pattern should be independently printed on each face of the hexahedron. It was also almost impossible to simultaneously print the patterns on plural faces of a polyhedron because simultaneous positioning of the patterns among printing blocks and plural faces of the polyhedron with a high precision was impossible.
The method for forming the conductive film either by plating, vapor deposition or sputtering comprises: a lift-off method in which the conductive film is formed after forming a resist film on the area where the conductive film is not formed on each face, followed by removing the resist film; and an etching method in which, after forming a conductive film on the entire surfaces on which the pattern is to be formed, a pattern of a resist film is formed on the foregoing film, followed by removing the conductive film in the area not covered with the resist film by etching.
However, since both methods described above require to form the resist film on each surface on which the pattern is to be formed, it was difficult to comply with the requirements of mass-production and low production cost.
Accordingly, the object of the present invention in view of the problems as set forth above is to provide a cheap antenna assembly suitable for mass-production, wherein a patterned conductive film is formed on the surface of a dielectric hexahedron.
In one aspect, the present invention for solving the foregoing problems provided an antenna assembly comprising a hexahedron of a dielectric material on each surface of which convex portions to serve as a circuit pattern are formed, wherein the circuit pattern comprising a conductive film is only formed on the convex portions.
In accordance with another aspect, the present invention provides a method for manufacturing an antenna assembly, wherein concave and convex portions are machined on the surface of a hexahedron of a dielectric material, and a desired pattern of a conductive film is formed on the convex portions using a roll coater.
The term xe2x80x9chexahedronxe2x80x9d as used herein denotes not only a cube or a rectangular parallelpiped column, but also any type of hexahedrons so far as they have six faces. However, any of the two faces among the six faces are preferably in a parallel relation one another in view of the spirit of the present invention. Such hexahedrons having concave and convex portions formed on the surfaces of a hexahedron such as a cube or a rectangular parallelpiped column, or those having hollow spaces also belong to the hexahedron according to the present invention.
While the dielectric material constituting the hexahedron desirably comprises a ceramic, glass or a mixture of a ceramic and glass in view of mechanical strength, any dielectric materials may be used so long as it is not contrary to the spirit of the present invention. Accordingly, plastics are acceptable for that purpose.
Although a film comprising a pure metal or metal alloy may be advantageously used as the conductive film, use of other conductive materials such as a conductive resin is also possible.
It is desirable in the present invention that the edge angle between the surface of the hexahedron and the inner wall of the concave portion is 80 degree or more and 135 degree or less. The edge may be chipped on the edge when the angle is less than 80 degree while, when the angle is larger than 135 degree, inner faces of the concave portion may be contaminated during deposition of the conductive film to compromise the function of the antenna. A edge angle of more than 90 degree and less than 120 degree is desirable when the function of the antenna is emphasized.
The conductive film should be continuously formed through the mutually adjoining faces on the hexahedron in the present invention, and the edges are desirably chamfered, because the conductive film formed by coating a conductive paste may be possibly interrupted at the edge when the edges are not chamfered. The radius of chamfering is desirably 0.1 mm or more and 0.5 mm or less. The effect of chamfering will be invalid when the radius of chamfering is less than 0.1 mm, while the conductive paste can be hardly spread on the chamfered edge during coating to rather interrupt the conductive film when the radius of chamfering is larger than 0.5 mm.